The goal of this project is to better understand the effects of the host cell and other co-factors on human retroviral replication and pathogenesis. Specifically, we have shown that HTLV-I/II has a broader host range than CD4+ T-cells with macrophages, brain microglia and CD3- natural killer cells also infectable in vitro with cell-free vitrus. One patient with large granular lymphocyte (LGL) leukemia with evidence of human T-cell leukemia/lymphoma virus (HTLV) infection was studied. Cloning and sequencing of amplified products showed the HTLV-II pol and pX sequences in patient DNA. However, our data show that most patients with LGL leukemia are not infected with prototypical HTLV-I or HTLV-II. The frequent reactivity of patient sera to HTLV-I/II gag protein p24 and to env protein p21e, however, suggests that a deleted or variant form of HTLV-I/II may be associated with LGL leukemia. The ability of HTLV-I molecular clones to produce infectious virions has not previously been demonstrated. Thus, an HTLV-I provirus originating from an adult T-cell leukemia patient, was cloned into a plasmid vector and designated pCS- HTLV. Primary and secondary cell-free transmissions into primary T-cell demonstrated that this is an infectious molecular clone of HTLV-I. With regard to HIV-I infection, it is now clear that i patients, there is an equilibrium between productive infection and latent infection. We are studying the mechanism(s) for this equilibrium using the monocyte/macrophage, a reservoir of HIV-I infection in AIDS patients, as the model cell type. In latently infected THP-1, a monocytoid cell line, infectious virus was made after 5-azacytidine exposure. Since this suggests that either cellular or viral methylation plays a role in HIV replication, we found an antiviral effect on HIV by 3-Deaza-nucleoside compounds, potent inhibitors of S-adenosylhomocysteine (AdoHcy) hydrolase, a key enzyme in cellular methylation processes. Unexpectedly, in comparing the therapeutic indice between the paired pre- and post-AZT treatment HIV-I isolates, DZNep displayed an increase of 3- to 40-fold in its potency against AZT-resistant HIV-I isolates. Also, monocytes from asymptomatic seropositive individuals contained latent HIV. After coculture of these monocytes with Con A-activated T-cells from HIV negative normal donors, these latent monocyte cultures expressed virus. In studying T-cell derived cytokines, we found that IL-4 and IL-13, although closely related in modulating monocyte function, can have divergent effects on HIV expression in monocytes.